Although several long-term studies of alcoholism and drug disorders in the general population exist, the long-term course of substance use disorder in patients with severe mental illness (i.e., dual diagnosis) is largely unknown. We have currently followed 223 adults with dual diagnosis in the New Hampshire Dual Diagnosis Study for 6-7 years with minimal attrition (85 percent with nearly complete data). By extending the study to 10 years of follow-up, the proposed project will yield unique data on the pattern, stability, prediction, timing, and correlates of remissions of substance use disorder in this population. We will also be able to examine treatment costs longitudinally. The 10- year data will allow us to chart the course of abstinence, asymptomatic use, remission, and recovery in dual-diagnosis patients. The study will increase our understanding of the relationships among substance disorder, clinical outcomes, and service costs. Longitudinal data will also allow us to examine several hypotheses from the literature regarding the effects of treatment and non-treatment experiences on the course of substance use disorder in this population. Specifically, we will examine response to new medications (such as olanzapine and naltrexone), prolonged intervals of close supervision (e.g., parole, conditional discharge, or living in a supervised setting), participation in peer support groups (such as dual-diagnosis groups or Alcoholics Anonymous), new sources of hope (like marriage, work, or religion), and medical illnesses related to substance disorder (e.g., gastritis). The results will be of interest to policy makers in many states that are replicating the model of integrated dual-diagnosis services that has been used in New Hampshire since 1988.